Acid-assisted reductive elimination as a route to platinum(II) products from platinum(IV) tris(pyrazolyl)borate reagents

A series of chiral cationic platinum(II) complexes of the type [kappa(2)-(( Hpz*BHpz*Pt-2(R)(L)]-[BAr'4] (R = Me, L = MeCN (3), (BuNC)-Bu-t (4), py (5) , CO (6), CH2=CH2 (7), PMe2Ph (8); R = Ph, L = MeCN (10); pz* = 3,5-dimethy lpyrazolyl, BAr'(4) = tetrakis(3,5-trifluoromethylphenyl)-borate) has been prepared. Protonation of Tp'PtMe2H (1) or Tp'PtPh2H (2) (Tp' = hydridotris- (3,5 -dimethylpyrazolyl)borate) occurs selectively at a pyrazole nitrogen a tom and induces reductive elimination of methane or benzene. Subsequent add ition of ligand, L, traps the platinum(II) intermediate and yields 3-8 and 10. Addition of 2 equiv of PMe2Ph led to the formation of trans-[kappa(1)-( (Hpz*)BHpz*(2))Pt(Me)(PMe2Ph)(2)][BAr'(4)] (9), a square-planar complex con taining a rare monodentate protonated tris(pyrazolyl)borate ligand. Deproto nation of the pyrazolium ring (present after protonation of 1 or 2 and trap ping with added ligand) led to the synthesis of neutral platinum(II) comple xes of the type Tp'PtR(L) (R = Me, L = MeCN (11), SMe2 (12), CO (13), CH2=C H2 (14); R = Ph, L = MeCN (15)). Complexes 11, 12, and 15 exhibit square-pl anar coordination with a bidentate Tp' ligand, while complex 14 is trigonal bipyramidal. Tp'PtMe(CO) (13) is present in solution in both isomeric form s. X-ray structure determinations for the cationic complexes 3 and 6-9 and the neutral square-planar complex 12 are reported.